h 


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Hawaii  Agricultural  Experiment  Station, 


HONOLULU 


E.  V.  WILCOX,  Special  Agent  in  Charge. 


PRESS   BULLETIN    INO.  29 


The  Management  of  Pineapple  Soils 


BY 

P.  KELLEY, 

CHEMIST 


INTRODUCTION. 


The  cultivation  of  pineapples  in  Hawaii  has  deve 
ing  the  past  fifteen  years  into  one  of  the  important  agi 
industries  of  the  islands.  This  crop  for  the  most  part  has  been 
grown  on  virgin  soils,  which  produced  large  yields  of  excellent 
fruit,  and  this  naturally  encouraged  a  rapid  expansion  of  the 
industry.  W nile  a  small  part  of  the  land  is  owned  by  the  grower, 
by  far  the  greater  part  of  the  crop  is  grown  on  leased  land. 
From  the  beginning  the  pineapple  growers  have  been  controlled 
largely  by  the  idea  of  getting  out  of  the  land  maximum  crops  at 
a  minimum  of  cost,  and  with  little  forethought  for  the  perma- 
nence of  the  industry  or  the  maintenance  of  the  soil.  Pineapples 
constitute  practically  the  only  crop  that  is  cultivated  on  these 
lands.  The  continuous  growing  of  any  one  crop  on  the  same  soil 
is  likely  to  be  attended  with  certain  difficulties  and  can  hardly 
be  said  to  belong  to  a  system  of  permanent  agriculture.  The 
more  especially  is  this  true  when  it  is  applied  to  soils  contain- 
ing large  percentages  of  finely  divided  ferric  hydrate  and  small 


lgTldS*W>ft,,,,''' 


amounts  of  humus;  soils  that  under  the  prevailing  conditions 
naturally  require  the  most  intelligent  management.  There  need 
be  little  cause  for  surprise,  therefore,  that  conditions  have  arisen 
which  at  the  outset  were  unsuspected  and  which  are  hindrances 
to  the  continued  welfare  of  the  industry. 

A  large  part  of  the  pineapple  crop  is  grown  on  the  upland 
plains  of  Oahu,  principally  in  the  Wahiawa  and  adjacent  dis- 
tricts. The  discussion  in  the  following  pages  has  been  drawn 
largely  from  observations  and  a  study  of  the  conditions  and  soils 
in  the  Wahiawa  district,  although  the  deductions  apply  equally 
well  to  similar  soils  throughout  the  islands. 

As  pointed  out  in  previous  Annual"  Reports  of  this  Station, 
pineapple  soils  have  been  the  subject  of  investigation  at  the 
Experiment  Station  for  more  than  two  years.  In  1909  a  pre- 
liminary report!  was  issued  in  which  it  was  pointed  out  that 
the  pineapple  soils  of  Oahu  may  be  divided  into  two  classes  as 
regards  color — viz.,  black  and  red  soils.  In  this  report  some  of 
the  peculiarities  of  the  black  soils  were  emphasized.  Since  then 
each  of  these  classes  of  soil  has  been  under  continued  investiga- 
tion, which  has  resulted  in  the  bringing  together  of  a  large 
amount  of  scientific  data.  In  the  present  bulletin  it  is  purposed 
to  present  the  more  practical  phase  of  this  work  in  so  far  as  it 
relates  to  the  management  of  the  red  soils.  What  follows, 
therefore,  has  no  reference  to  the  black  manganiferous  soils. 
The  failure  of  pineapples  there  is  due  to  altogether  different 
causes. 

THE    CONDITIONS   IN    THE    FIELDS. 

For  some  time  the  growers  have  realized  that  in  some  way 
not  definitely  understood  by  them,  their  soils  after  a  few  years 
of  cultivation  begin  to  show  indications  of  exhaustion.  In  gen- 
eral the  first  crop  and  the  one  or  more  rattoons  following  it  are 


*  For  the  chemical  composition  of  these  soils,  see  Hawaii  Sta.  An. 
Rept.  1909. 

t  Hawaii  Sta.  Press  Bui.  No.  23. 


quite  satisfactory,  but  subsequent  plantings  result  in  .dimin- 
ished harvests.  As  already  pointed  out,  pineapples  constitute 
practically  the  only  crop  that  is  cultivated  on  these  soils.  Before 
replanting  a  field  it  is  customary  to  haul  off  and  remove  all  of 
the  old  plants,  thus  taking  from  the  land  every  vestige  of  plant 
residue  produced  thereon.  From  15  to  24  months  being 
required  for  the  production  of  the  first  harvest,  followed  by  one, 
two  or  three  rattoon  crops  of  one  year  each,  makes  necessary  the 
continued  cultivation  of  the  land  for  three  or  four  years.  Gen- 
erally the  virgin  soil  is  porous  and  naturally  absorbs  and  drains 
away  excessive  rains  before  the  water  becomes  stagnant  in  the 
soil,  and  brings  about  a  water-logged  condition.  After  the  virgin 
soil  has  undergone  the  necessary  preparation  to  insure  good 
tilth,  it  is  granular  and  porous.  It  has  what  the  farmer  calls 
a  shotty  texture. 

After  a  few  years  cultivation,  however,  there  is  brought 
about  a  noticeable  difference  in  the  appearance  of  the  soil.  It 
loses  its  granular  texture,  tillage  becomes  more  difficult  and  nat- 
ural drainage  is  retarded.  Following  a  heavy  rain  the  soil 
becomes  compact,  and  dries  out  into  a  hard  mass  which,  unless 
it  is  cultivated  before  thoroughly  drying  out,  becomes  almost 
solid.  The  same  condition  may  be  brought  about  even  during 
the  early  growth  of  the  first  crop  by  an  overflow  of  the  ditches 
during  excessive  rains,  which  frequently  cause  the  pineapples  to 
show  a  stunted  growth  from  which  they  rarely  recover.  Usually 
the  second  planting  even  on  soils  that  produced  abundant  har- 
vests, results  in  greatly  reduced  yields. 

LACK    OF    DRAINAGE. 

The  reduction  of  the  pineapple-producing  power  of  these 
soils  has  called  for  inquiry,  both  by  the  farmer  and  by  the  Sta- 
tion. Various  expedients  such  as  fertilizers,  lime,  manure,  etc.. 
have  been  tried,  and  often  with  indifferent  success.  Without 
excluding  other  possible  factors  it  has  been  recognized  for  some 
time  that  the  fundamental  difficult v  is  associated  with  inade- 


quate  .drainage,  that  under  the  existing  conditions  the  water- 
holding  power  of  the  soil  becomes  greatly  increased,  that  perco- 
lation and  consequently  drainage  is  hindered  by  the  methods 
employed.  In  the  old  fields  there  are  generally  isolated  plants 
or  small  areas  that  are  more  thrifty  than  the  surrounding  plants. 
Close  examination  has  shown  that  the  more  thrifty  plants  are 
found  on  slight  elevations  such  as  a  back  furrow  or  ridge  made 
by  throwing  together  two  furrows,  etc.  Upon  pulling  up  the 
unthrifty  plants  the  roots  are  often  found  to  be  dead,  except 
perhaps  one  or  two  small  roots  near  the  surface.  Sometimes 
only  one  root  barely  beneath  the  surface  of  the  soil  is  the  only 
living  subaereal  part  of  the  plant.  The  underground  part  of 
such  plants  is  frequently  undergoing  putrefactive  decay,  and 
even  several  days  after  rains  they  may  be  surrounded  by  a  wet 
soil  containing  stagnant  water. 

The  pineapple,  like  all  cultivated  plants,  requires  free  circu- 
lating air  around  its  roots;  it  demands  oxygen  just  as  animal 
life  requires  it.  Probably  nothing  is  more  effective  in  prevent- 
ing proper  aeration  in  soils  than  stagnant  water,  or  a  water- 
logged condition  in  which  the  inter-spaces  or  pores  of  the  soil 
are  more  or  less  completely  filled  with  water.  Air  is  then 
largely  excluded,  the  necessary  oxygen  is  shut  out  and  condi- 
tions unfavorable  to  plant  growth  ensue.  Under  such  condi- 
tions the  soil  bacteria  can  not  perform  the  functions  so  neces- 
sary in  the  preparation  of  plant  food,  and  fertilizers  can  not  do 
their  normal  duty.  Evidently  the  development  of  roots  near 
the  surface  of  the  soil,  above  referred  to,  is  an  effort  by  the  plant 
to  secure  oxygen  through  its  absorptive  organs. 

The  introduction  of  surface  ditches  has  usually  been  bene- 
ficial, but  rarely  of  itself  restores  the  soil  to  its  original  fertility, 
and  not  even  when  used  in  conjunction  with  liberal  quantities  of 
high-grade  commercial  fertilizers.  It  has  been  suggested  that 
under  the  influence  of  a  tropical  sun,  continuous  cultivation 
would  bring  about  an  oxidation  of  the  soil  organic  matter. 
Humus,  as  is  well  known,  has  the  property  of  making  heavy 


soils  more  porous  and  thus  aiding  drainage,  and  if  the  humus 
should  become  decomposed  it  would  materially  afTect  these  lands. 
Experiments  have  shown,  however,  that  a  slow  decomposition 
of  the  humus  takes  place,  but  that  it  goes  on  at  such  a  slow  rate 
as  largely  to  preclude  it  as  the  principal  factor.  Likewise  the 
lack  of  available  plant  food,  important  as  it  may  be,  is  not  at 
the  bottom  of  the  difficulty,  for  literally  hundreds  of  experi- 
ments by  the  growers  and  the  Station  as  well,  where  all  sorts 
of  commercial  fertilizers  in  every  kind  of  mixture  have  been 
applied  in  various  quantities,  have  not  in  themselves  restored  the 
land.  It  is  true  the  nitrifying  power  of  the  soil  becomes  greatly 
reduced,  but  the  application  of  commercial  forms  of  nitrogen 
has  not  proven  effective. 

Mechanical  analyses  of  the  virgin  and  cultivated  soils  show 
that  the  ultimate  particles  that  constitute  the  soil  have  not  been 
materially  altered,  which  they  could  not  be  reasonably  supposed 
to  be.  The  ordinary  operations  of  cultivation  are  not  of  such 
nature  as  to  pulverize  and  grind  to  powder  the  coarser  particles 
of  the  soil.  The  mechanical  analysis  shows,  however,  that  when 
reduced  to  its  ultimate  particles  these  soils  contain  a  very  small 
percentage  of  grit  or  coarse  material,  and  a  relatively  high  per- 
centage of  clay  and  fine  silt.  They  are  what  would  be  classified 
as  heavy  clay  soils,  although  the  so-called  clay  is  of  a  different 
nature  from  true  clay  in  a  chemical  sense,  and  while  possessing 
some  of  the  same  properties,  behaves  in  other  senses  vastly  dif- 
ferent. The  word  clay  in  this  bulletin  is  used  in  a  physical 
sense  only,  and  has  reference  to  the  size  of  the  soil  particles. 

THE    CAUSE    OF    FAILURE. 

While  the  percentages  of  clay  or  other  constituents  are  not 
materially  different  in  the  new  and  old  soils,  the  degree  of  gran- 
ulation of  the  clay  is  greatly  modified.  The  virgin  soil  when 
shaken  with  a  column  of  water,  will  soon  settle  out,  leaving 
practically  a  clear  solution  above  it,  whereas  the  older  cultivated 


soils  when  so  treated  give  rise  to  a  turbid  solution  which  will 
not  settle  out  for  weeks. 

In  the  state  of  nature  where  good  tilth  is  attained,  the  par- 
ticles that  constitute  the  clay  content  of  a  soil,  particles  which 
when  separated  are  extremely  small  and  will  remain  in  suspen- 
sion in  water  almost  indefinitely,  are  collected  into  aggregates 
or  granules,  which  granules  act  as  units  and  impart  to  the  soil 
properties  in  every  way  similar  to  those  brought  about  by  ulti- 
mate particles  of  a  much  larger  size  than  clay.  The  bringing 
about  of  such  conditions  in  the  soil  is  variously  styled  grauula- 
tion,  nocculation,  coagulation,  etc.  It  is  an  important  function 
of  cultivation  to  aid  nature  in  cementing  the  clay  particles  into 
granules,  and  is  accomplished  by  admitting  sunlight  and  air, 
and  subjecting  the  soil  to  different  degrees  of  moisture,  carbonic 
acid,  etc. 

These  soils  are  frequently  cultivated  and  usually  well  pre- 
pared, but  instead  of  an  open  granular  structure  being  main- 
tained by  this  operation,  the  soil  steadily  becomes  more  difficult 
to  till,  drainage  is  hindered,  and  deflocculation  results.  The 
soil  is  simply  puddled.  What  are  the  causes  of  this  phenome- 
non? The  principal  causes  are  cultivation,  tramping  over  and 
otherwise  disturbing  the  soil  when  it  is  wet.  It  is  a  principle 
known  by  farmers  for  centuries  that  the  cultivation  of  clay  soils 
when  they  are  wet  injures  the  land  and  brings  about  conditions 
which  it  may  take  years  to  overcome.  The  intelligent  farmer  in 
older  agricultural  regions  will  only  as  a  last  resort  allow  the 
cultivation  of  his  clay  soils  when  they  are  wet.  In  the  cultiva- 
tion of  wet  clay  soils  the  loosely-bound  granules  become  broken 
up  and  separated  into  their  component  particles,  and  when  once 
the  bonds  of  union  are  severed,  it  is  by  no  means  easy  to  reunite 
them.  We  need  no  better  illustration  of  the  effects  of  tillage 
on  wet  soils  than  is  to  be  found  right  here  among  the  rice- 
growers,  who  deliberately  puddle  the  soil  by  working  it  when  it 
is  wet  in  order  the  better  to  prevent  loss  of  irrigation  water 
through  seepage  and  drainage. 


It  is  a  common  practice  in  the  pineapple  sections  of  the 
islands  to  cultivate  when  the  soil  is  practically  saturated.  At 
certain  times  heavy  rains  thoroughly  wet  the  land  and  these 
are  often  followed  by  strong  winds  and  a  hot  sun,  which  brings 
about  a  rapid  drying  of  the  surface.  Frequently  the  cultivators 
are  sent  into  the  fields  when  the  surface  seems  dry  enough  to 
cultivate,  but  the  soil  two  or  three  inches  below  the  surface  is 
wet  almost  to  saturation.  The  mere  trampling  of  the  soil  at 
such  times  when  continued  through  a  period  of  years  tends  to 
bring  about  deflocculation  of  the  clay  and,  therefore,  puddle  the 
soil,  so  that  effective  drainage  is  hindered. 

Puddled  soils  hold  water  tenaciously  and  under  such  condi- 
tions denitrification  instead  of  nitrification  may  take  place; 
effective  aeration  is  made  impossible  and  a  condition  unfavor- 
able for  pineapple  growth  follows.  The  application  of  fertilizers 
to  such  soils  is  almost  sure  to  result  in  disappointment,  because 
the  fundamental  difficulty  is  not  a  lack  of  plant  food.  Good 
tilth,  a  good  mechanical  condition  in  the  soil,  is  just  as  impor- 
tant as  available  plant  food,  and  in  its  absence  fertilizers  can 
not  perform  their  normal  function  and  bring  about  the  desired 
results.  In  some  instances  under  such  conditions  fertilizers  may 
even  prove  injurious,  titrates  in  water-logged  soils  may  be 
reduced  to  nitrites.  Such  changes  actually  take  place  in  some 
Hawaiian  soils,  and  nitrites  are  active  plant  poisons. 

Furthermore,  soils  that  contain  such  large  quantities  of 
finely-divided  ferric  hydrates  under  the  influence  of  putrefactive 
decay  may  be  reduced  to  ferrous  carbonate  and  sulphate,  either 
of  which  are  poisonous  to  many  plants. 

It  has  been  shown  in  other  countries  and  here  that  the  con- 
tinued use  of  nitrate  of  soda  on  clay  soils*  also  tends  to  bring 
about  a  deflocculation  of  the  soil,  and  where  it  has  been  so  used 
the  land  remains  wet  longer  after  rains.  The  same  condition 
may  arise  from  the  continued  use  of  certain  other  fertilizers.    In 


*  At  the  Rothamsted  Expt.  Sta.,  where  nitrate  of  soda  has  been  in 
continued  use  for  60  years,  a  deflocculation  of  the  soil  has  resulted. 
See  Jour.  Royal  Agr.  Soc,  Vol.  70,  1909,  pp.  12-35. 


the  pineapple  sections,  however,  such  fertilizers  have  not  come 
into  general  use.  In  fact,  no  fertilizer  has  been  used  in  many 
instances  where  the  soil  has  assumed  a  bad  condition.  It  has 
been  found,  however,  that  on  some  of  these  soils  the  application 
of  nitrate  of  soda  tends  to  aggravate  the  already  existing  troubles 
and,  therefore,  injures  rather  than  benefits  the  growth  of  pine- 
apples. 

REMEDIES. 

The  bringing  back  of  these  soils  into  a  condition  favorable 
for  pineapple  growth  can  not  be  accomplished  in  a  day  and  is 
far  easier  to  prevent  than  to  overcome  once  it  is  brought  about. 
With  the  virgin  soils  the  farmer  should  by  all  means  strive  to 
prevent  such  conditions.  Xo  heavy  clay  soils  should  ever  be 
cultivated  when  they  are  wet.  If  the  fields  demand  attention 
through  the  rapid  growth  of  weeds,  during  rainy  seasons,  it 
will  be  far  better  to  pull  out  the  weeds  by  hand  or  cut  them  off 
near  the  surface  with  hand  hoes.  The  results  of  cultivating  wet 
clay  soils  aside  from  that  of  checking  and  destroying  grass  and 
weeds,  are  positively  injurious  and  in  fact  really  hinders  one  of 
the  very  objects  of  tillage,  that  is  aeration. 

Air  and  sunshine  in  time  will  bring  about  granulation  of  the 
soil  and  by  thoroughly  stirring  it  at  intervals  when  fairly  dry, 
nature  may  be  aided  in  restoring  tilth.  This  should  always  be 
accompanied  by  the  best  possible  drainage  that  can  be  provided. 
When  this  has  been  clone  fertilizers  will  no  doubt  prove  effective 
and  can  be  used  profitably.  Barnyard  manure  will  also  aid 
nature  in  restoring  these  soils,  by  making  them  more  porous  and 
allowing  a  freer  circulation  of  air,  but  should  be  applied  some 
months  before  the  land  is  to  be  planted.  Lime  is  also  generally 
recommended  for  heavy  clay  soils  as  a  means  of  making  them 
more  friable  and  improving  their  tilth,  but  the  application  of 
lime  to  the  pineapple  soils  of  Wahiawa  has  at  least  failed  to 
show  any  advantage  to  be  derived  from  it.  Some  of  the  growers 
maintain  that  lime  makes  the  cultivation  of  the  soil  more  diffi- 


cult,  causes  it  to  remain  wet  longer  after  rains  and  brings  about 
poorer  drainage.  This  subject  is  now  under  investigation  but 
it  is  too  soon  to  draw  conclusions.  It  should  be  borne  in  mind, 
however,  that  while  these  are  called  heavy  clay  soils,  the  clay 
in  them  is  of  an  altogether  different  nature  from  the  clay  in 
most  countries,  and  it  is  not  inconceivable  that  lime  will  react 
in  a  manner  likewise  different.  If  lime  is  to  be  added  as  a 
means  of  correcting  acidity  or  for  other  reasons,  beach  sand  is 
recommended. 

It  will  be  far  easier  to  maintain  "condition"  in  these  soils 
under  a  system  of  rotation  of  crops.  In  fact,  some  of  the 
Wahiawa  soils  are  almost  sure  to  get  into  a  bad  mechanical  con- 
dition if  continuously  cultivated  in  the  same  crop.  It  is  doubt- 
ful whether  any  crop  can  be  most  successfully  grown  without 
rotation  on  soils  similar  to  these.  With  the  vast  majority  of 
cultivated  crops,  it  is  far  better  and  more  permanent  to  grow 
them  in  a  system  of  rotation.  Whatever  rotation  is  employed 
it  should  include  some  leguminous  crop  which  is  plowed  under. 
This  will  tend  to  improve  the  tilth  of  the  soil  and  at  the  same 
time  add  nitrogen,  an  important  and  deficient  element  in  these 
soils. 

SUMMARY  AND   CONCLUSIONS. 

The  continued  cultivation  of  pineapples  on  the  same  land 
has  already  brought  about  conditions  unfavorable  to  the  growth 

O  O  © 

of  the  crop.  The  use  of  fertilizers,  lime  and  manure  have"  not 
restored  this  soil  to  its  original  productivity.  The  mechanical 
condition  of  the  soil  becomes  greatly  affected  and  poor  drainage 
results. 

While  only  a  slight  change  has  taken  place  in  the  humus, 
the  clay  has  become  deflocculated,  thus  reducing  the  size  of  the 
pores  in  the  soil  and  effectually  hindering  drainage.  This  con- 
dition in  these  soils  is  brought  about  and  really  caused  by  culti- 
vating the  soil  when  it  is  wet.  In  some  instances,  however,  it 
has  been  caused  by  beating  rains,  accompanied  by  overflows.    In 


10 

such  puddled  soils  proper  aeration  is  impossible  and  bad  physi- 
cal, biological  and  chemical  conditions  prevail. 

The  best  remedy  is  that  of  prevention;  these  soils  should 
not  be  cultivated  when  wet,  for  damage  is  sure  to  result.  Sun- 
shine and  air  aided  by  thorough  tillage  when  the  soil  is  in  proper 
moisture  conditions  will  assist  nature  in  restoring  tilth.  The 
best  possible  drainage  should  be  provided  by  introducing  ditches 
at  short  distances  apart.  Manure,  especially  if  accompanied 
with  ample  aeration,  will  tend  to  make  the  soil  more  porous  and, 
therefore,  aid  drainage.  And  finally,  the  continued  cultivation 
of  the  land  in  pineapples  should  give  way  to  an  intelligent  system 
of  rotation. 


"lillipii 


